media: ov5640: Fix 720x480 in RGB888 mode

Adjust the left crop of 720x480 to enable capture in RGB888 format,
which is otherwise broken.

The 56 pixels alignment has been copied from the 720x576 mode.

Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>